1. Field of the Invention
This invention relates to the field of sidewall inspection of transparent and translucent bodies, and in particular to a video inspection system in which a succession of collimated elevation views are captured and processed for sorting the bodies, each view showing a plurality of successive bodies.
2. Prior Art
Video sidewall inspection systems are known in various forms in which a video camera is oriented perpendicular to a longitudinal axis of a back-lighted container, to capture and analyze data representing an image of container sidewalls, including both the front sidewall and a rear sidewall. Inasmuch as the view along the sides of the usually-cylindrical container is foreshortened, means are sometimes provided to simultaneously or sequentially secure at least two angularly spaced views around the container to cover the whole surface. Such systems are known to detect defects in the sidewall surfaces, dirt, chips and unusual wear. Examples of sidewall inspection systems can be found, for example, in U.S. Pat. Nos. 3,746,784 and 4,002,823, both to Van Oosterhout, 4,136,930--Gomm et al and 4,376,951--Miyazawa. Insofar as these patents teach processing of data, their disclosures are incorporated.
Video inspection systems take various approaches to the problems of detecting and sorting containers based on their quality, cleanliness, etc. The present invention is concerned with capturing instantaneous views of each successive container from a plurality of angularly-spaced positions. The invention is equally applicable to any of the various forms of analysis, such as those in which areas of contrast are analyzed to detect chips or dirt, or a container is twisted or agitated to produce a relative movement of contrasting foreign material in or on the container.
A video image of a container to be be analyzed is a two dimensional data pattern representing one or more images focused on a plane surface. Prior art inspection systems have attempted to collect an enlarged two dimensional image of container sidewalls by rolling a container in front of a linear or planar detector, but the image is necessarily a two dimensional pattern. The present invention relates to optimizing the data capture in several ways. Using cameras directed at only one inspection field, simultaneous data is captured in which each backlighted container is recorded, rolled ahead to a next successive position within the inspection field and again recorded from the new angular aspect, etc. The data processor of the invention rejects containers for defects in any view, and preferably correlates the images of one container from the successive views to analyze for defect patterns, taking care to appropriately handle gaps in the views occurring when processing leading and trailing containers in a line.
Collection of a two dimensional simultaneous view of a plurality of containers has certain costs and certain benefits. The simultaneous view allows the user to continue to transport containers along a conveyor in front of one recorder station, rather that stopping for recordation of a data image or using spaced stations. In order to accomplish such a feat for a plurality of containers to be recorded simultaneously, the invention provides a large diffuse backlighted area in which the backlighting is sufficiently even to allow a high resolution examination of the image for variations in brightness indicative of dirt, wear or damage. Moreover, a true elevation view is recorded.
Processing an image of an item having more than a trivial depth in the viewing direction presents certain problems of perspective. Prior art systems have attempted to resolve viewing problems by providing extensive optics to provide a substantially perpendicular view of a sidewall for inspection. An example of such a system is found in U.S. Pat. No. 3,932,042-Fanni, et al, in which various lenses and reflectors are used to facilitate recordation of an image of a single bottle from angularly spaced perpendicular directions through the sidewall. A split image technique is employed together with substantially-parabolic reflectors disposed adjacent light sources, in a effort to provide even backlighting and a substantially elevational view. Such optical systems may be effective, but are prone to difficulty in that any sophistication in optics means expensive hardware, and will require a great deal of maintenance to maintain the necessary precision of alignment, cleanliness of elements and the like.
Perspective effects in an image recorded by a video camera viewing a cylindrical container or the like can have a substantial impact on analysis of transparent or translucent bodies. Perspective views are characterized by relatively larger foreground features due to the diverging lines along which the effective point light receptor (i.e., the video camera) views the container. Should either the foreground or background sidewall present an opaque label or other feature that interferes with analysis because the other sidewall cannot be viewed, the divergence of perspective viewing lines rays results in a larger obstruction in perspective viewing than for a true elevation view. The obstructed or obstructing field of the rear sidewall is larger than that of the front sidewall. For example, in order to detect faults in a given area on the front sidewall, it is necessary to ensure that no opacity such as a label appears on a larger area of the rear sidewall that would be traced by diverging rays from the video detector. A perspective view of the container also has the inherent difficulty that certain portions of each sidewall (e.g., near the bottom edge) are not subject to inspection due to their association with portions visible through the sidewall that cannot be inspected due to opacities other than defects.
It is theoretically possible to reduce problems with perspective viewing by providing a very long focal length view of a container being inspected. For example, a telephoto lens viewing the container would effectively view the container from a longer distance, thereby providing less-divergent viewing lines and a more elevational view. This is a theoretical solution to perspective problems, but may not be practical. Telephoto lens optics are expensive and heavy, and can be subject to problems with dirt in a production environment. Furthermore, in order to provide a relatively large field of view, for example to minimize the number of cameras required to cover a field and/or to record simultaneously the image of a number of containers positioned successively on a conveyor, such a telephoto viewing system would either have to be positioned at a substantial distance from the containers being inspected, or would be very heavy and expensive in the optical hardware needed to ensure good resolution, good light transmission, etc.
The present invention provides a true elevation view of a plurality of containers simultaneously, preferably using only one upper and one lower video camera, and collimating the image of the successive containers. The collimating is preferably accomplished using a fresnel lens, whereby the weight and expense of the collimator are minimized. A fresnel lens in this application tends to disrupt the image of the container as it appears to the eye due to the ridged nature of a fresnel lens. However, this apparent degradation of the image is substantially outweighted by the benefits inherent in providing a true elevation view of the container. Moreover, lens ridge effects are subject to removal by analysis techniques in which the brightness of pixels is statistically analyzed.
Together with a means for continuously rolling bottles moving along the container, the invention records upper and lower images of three successive containers, and correlates the data from these images to analyze and segregate containers for any defects such as dirt, wear, bird's wings, etc. The invention is accordingly quite effective yet the expense of providing a true elevation view is minimized by the relatively inexpensive optics and the need for only one or two video cameras successively recording images of a series of adjacent containers.